From United States patent application Ser. No. 08/050,085, filed Apr. 28, 1993, and U.S. Pat. No. 5,325,740, it is known to maintain the output torque of an automatic transmission at the same level before and after a gear-shifting operation of the automatic transmission by means of a deliberate control of the engine torque, provided the driver command does not change during the shifting of the gear. The term "output torque" used herein refers to the output torque of the transmission. The output torque and thus the traction force at the drive wheels is controlled in such a way that it is, within wide limits, independent of the gear just engaged or the state of the converter lockup clutch. This method is known under the name "Mastershift". With the aid of this known control function, the gear-shift points of the automatic transmission can be positioned in areas which are optimal for consumption without at the same time having to accept losses in terms of handling and the ability to meter traction force. However, the known control function relates exclusively to the control of the output torque outside the gear-shifting operations.
In United States patent application Ser. No. 08/157,993, filed Nov. 26, 1993, a method and an apparatus for controlling a vehicle are described in which an interface is defined between different subsystems (of which one is an engine control system) toward the engine control system. This interface operates on the basis of the torque produced by the engine and the subsystems exchange via the interface information relating to this torque in order to control the vehicle.
U.S. Pat. No. 5,407,401 discloses how the clutches of the automatic transmission and the torque of the engine of the vehicle can be controlled so that the output torque after the gear-shifting operation is approximately the torque present before the gear-shifting operation. For this purpose, various control sequences are provided depending on whether the operation is a shifting-up or shifting-down operation. It is essential here that the control sequences described for keeping the output torque constant during gear-shifting operations only apply when the vehicle is in an operating state with a positive clutch torque. Such an operating state with positive clutch torque occurs during a so-called engine traction operation, that is, the vehicle is driven on the basis of the engine torque.
Furthermore, it is known that, in addition to the above-mentioned engine traction operation, operating states with a negative clutch torque can also be present in a vehicle. In such engine overrun operating modes, the engine is driven by the wheels of the vehicle. The engine then supplies an engine braking torque.
The object of the present invention is to ensure optimum control of the output torque during gear-shifting problems of an automatic transmission in all operating states.